An Optical Transport Network (OTN) transfer method defined in the International Telecommunication Union-Telecommunication Standardization Sector (ITU-T) G.709 specification is a method by which client signals flowing into an optical network are stored into and transferred as an Optical channel Transport Unit (OTU). In addition to a payload storing the client signals therein, an OTU stores therein an overhead (OH) of an Optical channel Payload Unit (OPU) and an OH of an Optical channel Data Unit (ODU).
According to the OTN transfer method, it is possible to arrange a plurality of types of client signals having mutually-different transfer rates to be stored into a single signal. A plurality of types of OTUs are defined. For example, it is possible to arrange client signals up to approximately 1.25 Gbps to be stored into an OTU0 and to arrange client signals up to approximately 2.5 Gbps to be stored into an OTU1. Further, it is possible to arrange client signals up to approximately 10 Gbps to be stored into an OTU2, to arrange client signals up to approximately 40 Gbps to be stored into an OTU3, and to arrange client signals up to approximately 100 Gbps to be stored into an OTU4. Each of the OTUs is able to store a plurality of types of ODUs therein.
As for the plurality of types of ODUs, for example, it is possible to arrange client signals up to approximately 1.25 Gbps to be stored into an ODU0 and to arrange client signals up to approximately 2.5 Gbps to be stored into an ODU1. Further, it is possible to arrange client signals up to approximately 10 Gbps to be stored into an ODU2, to arrange client signals up to approximately 40 Gbps to be stored into an ODU3, and to arrange client signals up to approximately 100 Gbps to be stored into an ODU4.
Each of the ODUs is configured to be able to store therein one or more ODUs at a lower level. For example, an ODU4 is able to store therein one or more ODUs selected from a group made up of ODU0s, ODU1s, ODU2s, and ODU3s, whereas an ODU3 is able to store therein one or more ODUs selected from a group made up of ODU0s, ODU1s, and ODU2s. In addition, each of the ODUs is configured so as to implement a multi-stage method by which each ODU is able to store therein ODUs positioned at lower levels that are nested on multiple stages. In this situation, an ODU storing therein one or more ODUs positioned at one or more lower levels will be referred to as a High-Order ODU (HO-ODU). In contrast, an ODU storing therein no ODUs positioned at lower levels will be referred to as a Low-Order ODU (LO-ODU). An ODU4 implementing the multi-stage method is obtained by, for example, multiplexing together two HO-ODU2s each of which stores therein eight LO-ODU0s and two HO-ODU3s each of which stores therein four LO-ODU2s.
Further, a separating unit included in a transfer apparatus compliant with an OTN is configured to extract LO-ODU data from HO-ODUs in an OTU received from the OTN. FIG. 16 is a drawing for explaining an exemplary operation to extract LO-ODU data from HO-ODUs in an OTU. In the present example, for the sake of convenience in the explanation, the OTU is assumed to be an OTU4. The OTU4 stores therein an ODU4, whereas the ODU4 stores therein HO-ODU3s (#1, #2) and HO-ODU2s (#1, #2). Further, the HO-ODU3 (#1) stores therein LO-ODU2s (#1 to #4), while the HO-ODU3 (#2) stores therein LO-ODU2s (#5 to #8). The HO-ODU2 (#1) stores therein LO-ODU0s (#1 to #8), while the HO-ODU2 (#2) stores therein LO-ODU0s (#1 to #8).
A separating unit 100 illustrated in FIG. 16 includes an ODU4 separating unit 101, two ODU3 separating units 102, eight ODU2 separating units 103, two ODU3 processing units 104, eight ODU2 processing units 105, and a selector 106.
The ODU4 separating unit 101 is configured to extract the HO-ODU3s and the HO-ODU2s from the HO-ODU4 and also to extract High-Order Multiplex Structure Identifier (HO-MSI) information indicating a mapping configuration on the inside of the HO-ODU4. The HO-MSI information of the HO-ODU4 is configured with 80 Tributary Slots (TSs) and manages MSI information indicating a mapping configuration of all the LO-ODUs included in the ODU4 in units of TSs. Further, each of the TSs is configured to identify a payload region storing therein the data of a corresponding one of the LO-ODUs included in the OTU. In other words, each of the TSs is configured to identify the LO-ODU stored in a corresponding payload region.
Each of the ODU3 separating units 102 is configured to extract the LO-ODU2s from a corresponding one of the HO-ODU3s extracted by the ODU4 separating unit 101 and to extract Low-Order Multiplex Structure Identifier (LO-MSI) information of the HO-ODU3. The LO-MSI information of each of the HO-ODU3s is configured with 32 TSs and manages the MSI information of all the LO-ODUs included in the ODU3, in units of TSs.
Each of the ODU2 separating units 103 is configured to extract the LO-ODU0s from a corresponding one of the HO-ODU2s extracted by the ODU4 separating unit 101 and to extract the LO-MSI information of the HO-ODU2. The LO-MSI information of each of the HO-ODU2s is configured with 8 TSs and manages the MSI information of all the LO-ODUs in the ODU2, in units of TSs.
Each of the ODU3 separating units 102 is provided with a different one of the ODU3 processing units 104. Each of the ODU3 processing units 104 is configured to monitor an OH or the like in the corresponding HO-ODU3 and to extract data of the LO-ODU2s included in the HO-ODU3, for each MSI value in units of TSs. Each of the ODU2 separating units 103 is provided with a different one of the ODU2 processing units 105. Each of the ODU2 processing units 105 is configured to monitor an OH or the like in the corresponding HO-ODU2 and to extract data of the LO-ODU0s included in the HO-ODU2, for each MSI value in units of TSs.
Next, an example of an operation performed by the separating unit 100 will be explained. The ODU4 separating unit 101 extracts the HO-ODU3s (#1, #2) and the HO-ODU2s (#1, #2) from the HO-ODU4, also extracts the HO-MSI information of the HO-ODU4 corresponding to the 80 TSs, and further informs the selector 106 of the extracted HO-MSI information.
An ODU3 separating unit 102A extracts the LO-ODU2s (#1 to #4) from the HO-ODU3 (#1) and also extracts the LO-MSI information of the HO-ODU3 (#1) corresponding to the 32 TSs. Further, the ODU3 separating unit 102A informs an ODU3 processing unit 104A corresponding to the ODU3 separating unit 102A of the LO-MSI information. FIG. 17A illustrates the LO-MSI information corresponding to the ODU3 separating unit 102A. TSs 1 to 8 correspond to the LO-ODU2 (#1) and the MSI values thereof are each “80hex”. TSs 9 to 16 correspond to the LO-ODU2 (#2) and the MSI values thereof are each “81hex”. Further, TSs 17 to 24 correspond to the LO-ODU2 (#3) and the MSI values thereof are each “82hex”. TSs 25 to 32 correspond to the LO-ODU2 (#4) and the MSI values thereof are each “83hex”. The “hex” indicates a hexadecimal expression.
Further, an ODU3 separating unit 102B extracts LO-ODU2s (#5 to #8) from the HO-ODU3 (#2) and also extracts the LO-MSI information of the HO-ODU3 (#2) corresponding to the 32 TSs. Further, the ODU3 separating unit 102B informs an ODU3 processing unit 104B corresponding to the ODU3 separating unit 102B of the LO-MSI information. FIG. 17B illustrates the LO-MSI information corresponding to the ODU3 separating unit 102B. TSs 1 to 8 correspond to the LO-ODU2 (#5) and the MSI values thereof are each “80hex”. TSs 9 to 16 correspond to the LO-ODU2 (#6) and the MSI values thereof are each “81hex”. TSs 17 to 24 correspond to the LO-ODU2 (#7) and the MSI values thereof are each “82hex”. TSs 25 to 32 correspond to the LO-ODU2 (#8) and the MSI values thereof are each “83hex”.
An ODU2 separating unit 103A extracts the LO-ODU0s (#1 to #8) from the HO-ODU2 (#1) and also extracts the LO-MSI information of the HO-ODU2 (#1) corresponding to the 8 TSs. Further, the ODU2 separating unit 103A informs an ODU2 processing unit 105A corresponding to the ODU2 separating unit 103A of the LO-MSI information. Further, an ODU2 separating unit 103B extracts the LO-ODU0s (#1 to #8) from the HO-ODU2 (#2) and also extracts the LO-MSI information of the HO-ODU2 (#2) corresponding to the 8 TSs. Further, the ODU2 separating unit 103B informs an ODU2 processing unit 105B corresponding to the ODU2 separating unit 103B of the LO-MSI information.
On the basis of the LO-MSI information received from the ODU3 separating unit 102A, an ODU3 processing unit 104A extracts data of the LO-ODU2s (#1 to #4) from the LO-ODU3 (#1). After that, the ODU3 processing unit 104A outputs the data of the LO-ODU2s (#1 to #4) to the selector 106. Further, on the basis of the LO-MSI information received from the ODU3 separating unit 102B, the ODU3 processing unit 104B extracts data of the LO-ODU2s (#5 to #8) from the LO-ODU3 (#2). After that, the ODU3 processing unit 104B outputs the data of the LO-ODU2s (#5 to #8) to the selector 106.
On the basis of the LO-MSI information received from the ODU2 separating unit 103A, the ODU2 processing unit 105A extracts data of the LO-ODU0s (#1 to #8) from the LO-ODU2 (#1). After that, the ODU2 processing unit 105A outputs the data of the LO-ODU0s (#1 to #8) to the selector 106.
Further, on the basis of the LO-MSI information received from the ODU2 separating unit 103B, the ODU2 processing unit 105B extracts data of the LO-ODU0s (#1 to #8) from the LO-ODU2 (#2). After that, the ODU2 processing unit 105B outputs the data of the LO-ODU0s (#1 to #8) to the selector 106. The selector 106 is able to output the data of the LO-ODU2s (#1 to #8), the LO-ODU0s (#1 to #8) in the HO-ODU2 (#1), the LO-ODU0s (#1 to #8) in the HO-ODU2 (#2), i.e., the data of the LO-ODUs in the ODU4 corresponding to the 80 TSs.    Patent Document 1: Japanese Laid-open Patent Publication No. 2011-146917
When the data of the LO-ODUs is output from the ODU4, because the data of the LO-ODUs corresponding to the 80 TSs is to be output from the ODU4, it is sufficient to provide the transfer apparatus with ODU processing units configured to process the data corresponding to the 80 TSs. However, in consideration of patterns of combinations of the plurality of types of ODUs that can be stored in the ODU4, the transfer apparatus provides for an ODU processing unit 104 (105) for each of the ODU3 separating units 102 and the ODU2 separating units 103. As a result, the transfer apparatus provides for the ODU processing units 104 and 105 corresponding to 144 TSs at maximum, which are namely ODU3 processing units (64 TSs) corresponding to two HO-ODU3s and ODU2 processing units (80 TS) corresponding to ten HO-ODU2s. Consequently, the transfer apparatus includes a large number of ODU processing units that are not used, which makes the circuit scale large and increases the electric power consumption.